Selective Monitoring of Organophosphorus Pesticides by 31P-NMR Spectroscopy: Application to Purity Assay of Technical Products and Concentration Determination of Formulated Samples

31P nuclear magnetic resonance (NMR) was used as a highly selective, rapid and suitable analytical tool for the simultaneous identification and determination of five important organophosphorus pesticides (OPPs), without any sample preparation, in technical and formulation samples. The quantitative works of 31P-NMR spectroscopy were performed in the presence of phosphoric acid as a suitable internal standard. Linear working range for the analysis of trichlorfon, chlorpyrofos, fenithrothion, diazinon and glyphosate was 25–300 mg L−1. Limit of detection (at S/N = 3) for the proposed method, under the optimized experimental conditions, was found to be about 3 mg L−1 for the first four OPPs and 16.3 for the last one. The proposed method was applied to the analysis of a glyphosate formulation and two trichlorfon and chlorpyrofos technical samples. There was excellent agreement between the results by 31P-NMR and those by the standard methods. The proposed method is rapid, simple and safe, as toxic samples are analyzed ‘as received’ without sample pre-treatment, permitting the routine analysis of pesticides in real samples.